1. Field of the Invention
The present invention relates to a preview apparatus (for confirming the depth of field) in a single lens reflex camera.
2. Description of the Related Art
A preview apparatus in a single lens reflex camera, in which the diaphragm (aperture-stop) is mechanically and manually controlled using a preview lever (manual lever) by a photographer is well known. In general, the diaphragm is continuously biased with a relatively large biasing force into a full open position. Therefore, it is necessary for a photographer use a large force in order to actuate the preview lever against the biasing force. It is difficult or the photographer to maintain the diaphragm in a stop-down position for a long period of time. A retainer mechanism to retain the diaphragm in the stop-down position is also well known. However, the photographer has to go to the trouble of setting and resetting the retainer mechanism each time.
To solve this, the assignee of the present application has proposed a motor-driven preview apparatus using a motor which is adapted to move a mirror and which is actuated by an electric switch (Japanese Unexamined Patent Publication No. 2-77045 or U.S. Pat. No. 5,257,052 corresponding thereto). In this preview apparatus, a mirror driving motor and a one-turn cam gear associated with the motor are provided, so that when the cam gear rotates in the forward direction, the preview operation and the release operation are sequentially carried out. When the preview switch is turned ON, the motor is rotated in the forward direction. Consequently, the stop-down operation is completed by the diaphragm drive mechanism which is associated with the motor, prior to the upward movement of the mirror. When the diaphragm is stopped-down at a predetermined position, the motor is stopped, so that the depth of field can be confirmed through the view finder. When the preview switch is turned OFF, the motor is reversed to reset the diaphragm.
With this structure, in general, the upward movement of the mirror begins after the stop-down operation of the diaphragm is completed upon releasing, and hence there is a considerable time lag between the operation of the release button and the movement of the shutter.
In an object of the present invention to provide a simple preview apparatus in a single lens reflex camera in which the preview operation is carried out by a motor which is driven in accordance with the operation of an electrical switch member, wherein there is little time lag between the operation of the release button and the movement of the shutter, upon normal releasing.